It is known to vaccinate day old chicks against Newcastle disease and bronchitis employing a combination of subcutaneous vaccination and simultaneous aerosol exposure.
Three types of supplementary aerosol vaccination methods have been proposed. One such method, hand spraying, is carried out with the aid of a small compression sprayer and employs a highly diluted spray usually containing about five doses per milliliter. The operator atomizes the spray fluid above and in the direction of boxes containing the chicks. This method has the disadvantage that functional spray parameters such as exposure time and application height are dependent on the operator and are not replicable. Furthermore, an ambient climatic condition such as relative humidity is not necesarily maintained constant and changes therein may produce changes in drop size due to evaporation.
Additionally, in some sprayers the pressure is not maintained constant, thus varying the droplet size spectrum and feed rate. In other sprayers, the droplet size is sufficiently small that a considerable part of the sprayed fluid is in drop sizes which are within the respiratory range of the chicks, that is, they are directly inhaled by the chick and probably reach the air bag system and the alveoli. The respiratory range for day old chicks is estimated to be particles having an aerodynamic diameter of less than 10-12 microns. This naturally causes vaccine to be wasted, and may cuase damage to the chicks.
A second method of supplementary aerosol spraying employs an automatic spray bar. This is a relatively automated technique wherein boxes, each containing approximately fifty chicks, are placed on a running belt and pass under a stationary spray bar. The output rate, spray height, exposure time, and range of droplet sizes are generally constant. However, ambient environmental conditions may vary and thus variations in the droplet size may occur, with the attendant possibility that droplets may fall within the respiratory range.
A third method of supplementary aerosol spraying employs a manually operated spray cell which is sized to accomodate a box containing about fifty chicks. A spray nozzle is affixed to the top of the cell and is fed with vaccine via a metering device, thus assuring a constant dose to the exposed chicks. The drop size range and its volume median diameter (VMD) is determined by the spray nozzle and its operating pressure. Although this method overcomes some of the difficulties mentioned above in connection with other methods, it does have the disadvantages that it is relatively wasteful in vaccine due to the use of a relatively large droplet VMD in order to avoid the harmful effects of evaporation, and further that it has a limited treatment capacity.